System and method for releasing tooth positioning appliances

ABSTRACT

An improved dental appliance system, and methods for using and fabricating the improved appliance, including a polymeric overlay or shell having a teeth-receiving cavity formed therein. The dental appliance having the necessary stiffness or strength to firmly secure the appliance on the teeth and provide controlled forces required for repositioning the teeth, until such time as removal of the appliance is desired. The appliance may be configured for use with a removal mechanism. The removal mechanism provides for selective release of the appliance from the teeth as the removal mechanism undergoes a state change stimulated by an environmental stimulus or environmental switch.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] The present application is a continuation of application Ser. No.09/757,385 (Attorney Docket No. 018563-000520/AT-00006.1) filed Jan. 8,2001, which was a continuation of U.S. application Ser. No. 09/250,962(Attorney Docket No. 018563-000510/AT00006), filed Feb. 16, 1999, whichclaimed the benefit and priority of U.S. Provisional Patent ApplicationNo. 60/110,189 (Attorney Docket No. 018563-000500-AT00005), filed Nov.30, 1998. The full disclosures of which are hereby incorporated byreference for all purposes.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention is related generally to the field oforthodontics. More particularly, the present invention is related toimproved dental appliances and systems, and methods for using and makingthe same.

[0004] Elastic positioners optionally in combination with attachments tothe patient's teeth are employed in orthodontic treatments forcontrolled tooth movement to a pre-determined position. In providingsuch appliances and treatments, it is important to move teeth to anideal pre-determined position with gentle controlled forces. Typically,the appliance is fabricated to provide accuracy of placement incompliance with the exact shape of the teeth or the exact shape andplacement of the attachment device.

[0005] The use of elastic positioners for repositioning teeth is known.Such elastic positioners comprise a thin shell of elastic material thatgenerally conforms to a patient's teeth but is slightly out of alignmentwith the initial tooth configuration. By properly choosing theconfiguration, placement of the elastic positioner over the teeth willmove individual teeth to desired intermediate or final positions overtime. Of particular interest to the present invention, a systemcomprising multiple elastic tooth positioning appliances for performingorthodontic procedures is described in published PCT applicationW098/58596 which corresponds to co-pending application Ser. No.08/947,080, assigned to the assignee of the present application.

[0006] The resilient repositioning forces required to move a tooth fromone position to another position in a reasonable amount of time may beformidable. The design of appliances capable of imparting such forceswith acceptable comfort and appearance has been a challenge. To achievesuch forces, the appliance must be relatively stiff (i.e. possess a highstrength or high modulus) to provide a sufficient grip on the teeth. Thestiffness both ensures that the dental appliance remains firmly inposition on the patient's teeth and provides the repositioning forcenecessary to move the teeth. The stiffness also permits the dentalappliance to “grab hold” of an anchor device or other surface featurewhich may be present on the tooth to apply a directed force to executeorthodontic tooth movements.

[0007] While appliance stiffness is desirable for providingrepositioning forces and for maintaining appliance position on theteeth, the removal of stiff appliances can be difficult. Toothpositioners which are stiff and tightly conform to the teeth can requirethe use of orthodontic tools for removal, making removal by the patientvery difficult. Periodic removal is desirable for a number of purposesincluding cleaning, dental hygiene, removal before meals, removal forcosmetic purposes, and removal and replacement in the course oftreatment. In most or all of these cases, however, it will beinconvenient for the patient to visit the practitioner. Moreover, theuse of tools can damage the appliance, making its reuse difficult orimpossible.

[0008] For these reasons, it would be desirable to provide alternativemethods, appliance designs, and systems for removing a dental appliancefrom the teeth. Such methods and apparatus, systems should be economicaland, in particular, should reduce the difficulty experienced and theamount of time required by the practitioner and/or patient in removingand subsequently re-applying the appliance. At least some of theseobjectives will be met by the methods and systems of the presentinvention described hereinafter.

[0009] 2. Description of the Background Art

[0010] W098/5896 and co-pending application Ser. No. 08/947,080 arereferenced above. Tooth positioners for finishing orthodontic treatmentare described by Kesling in the Am. J. Orthod. Oral. Surg. 31:297-304(1945) and 32:285-293 (1946). The use of silicone positioners for thecomprehensive orthodontic realignment of a patient's teeth is describedin Warunek et al. (1989) J. Clin. Orthod. 23:694-700. Clear plasticretainers for finishing and maintaining tooth positions are commerciallyavailable from Raintree Essix, Inc., New Orleans, La. 70125, andTru-Tain Plastics, Rochester, Minn. 55902. The manufacture oforthodontic positioners is described in U.S. Patent Nos. 5,186,623;5,059,118; 5,055,039; 5,035,613; 4,856,991; 4,798,534; and 4,755,139.

[0011] Other publications describing the fabrication and use of dentalpositioners include Kleemann and Janssen (1996) J. Clin. Orthodon.30:673-680; Cureton (1996) J. Clin. Orthoclon. 30:390-395; Chiappone(1980) J. Clin. Orthodon. 14:121-133; Shilliday (1971) Am. J.Orthodontics 59:596-599; Wells (1970) Am. J. Orthodontics 58:351-366;and Cottingham (1969) Am. J. Orthodontics 55:23-31.

BRIEF SUMMARY OF THE INVENTION

[0012] The present invention provides improved dental appliances andmethods for using and fabricating such appliances. Individual appliancescomprise a polymeric shell having a teeth-receiving cavity formedtherein. The shell will have the necessary stiffness to firmly securethe appliance on the teeth and provide controlled forces required forrepositioning the teeth. As discussed in detail below, one or moreremoval features or mechanisms will be provided to facilitate removal ofthe appliances from the teeth. The removal mechanism may be an integralproperty or characteristic of the shell and/or may be a separatecomponent or components in addition to the shell. Exemplary shellproperties include changes in stiffness or shape induced by exposure ofthe shell to different environmental conditions, e.g. a change intemperature, a change in pH, a change in ionic strength, or the like.Exemplary additional components include adhesives, interface layers(between the shell and the tooth), tooth anchors, reinforcementcomponents (layers, filaments, braids, etc.), where such components canchange stiffness, dimensions, orientations, or the like to selectivelyhold or release the shell onto the teeth. Usually, the changes in theadditional components will be induced by the same types of environmentalchanges used for inducing property changes in the shell. Alternatively,removal mechanisms comprising separate components could be stimulated byexposure to an external energy source, e.g. being mechanically,electrically, optically, magnetically or otherwise triggered to induce achange which causes or permits release of the shell from the teeth.

[0013] Use of such removal mechanisms is advantageous in a number ofrespects. Environmental changes can be easily implanted by apractitioner or patient. For example, the practitioner or patient canwash the mouth with an appropriately heated, pH-modified, ionic strengthcontrolled, or other solution which can induce the desired change in theremoval mechanism. While the use of mechanically, electrically, oroptically triggered removal mechanisms may require additional equipment,such mechanisms can also be very simple and suitable for use by thepatient as well as the practitioner. In all cases, the removalmechanisms can usually be made reversible, i.e. the appliance can be“switchable” between attached configurations where the appliance willremain in place on the teeth and a release configuration where theappliance can be removed form the teeth. This is a particular advantagesince is allows the appliance to be temporarily “reconfigured” andremoved for any purpose and then repositioned over the teeth to continuethe treatment.

[0014] In a first aspect of the invention, a state change reduces thestiffness or shape (or both) of the shell material such that theengagement forces between the shell and the teeth or other interfacesare reduced or eliminated. The state change can be a change in anymaterial property which affects stiffness or shape, such ashardness/softness (as measured by durometer), elasticity, phase (as withshape memory polymers and materials), or the like. Preferably, the statechange will be reversible so that the shell can recapture the stiffnesslost or recover the shape which was lost while undergoing the initialstate change. The reduction of stiffness will usually comprise asoftening and/or increasing elasticity of the shell material, permittingthe shell to become more easily pulled from over the teeth. A change inshape will reduce or eliminate engagement forces between the applianceand the teeth or other interfaces due to an expansion, contraction,partial opening, reduction of interference, or other reconfiguration ofthe appliance. The desired state change will preferably be induced by anenvironmental change which can easily be effected in the patient'smouth. Preferred environmental changes are these which can beimplemented by a simple mouth wash with a solution having a particularcomposition, pH, temperature, ionic strength or other property. Theselected property should be one that the patient will not normallyencounter in daily life, at least during periods when release of theappliance is not intended. For example, temperature would not be a goodchoice unless it is intended that the appliance be removed when eatingor drinking hot foods and drinks. The property should also be one thatis physiologically acceptable, e.g. very high or very low pH might notbe desirable.

[0015] It is not necessary, however, that the “released” configurationbe long term or sustainable. In many instances, the removal mechanismwill permit mounting of the appliance onto the teeth when the removalmechanism is in its “attached” configuration. To remove the appliance,the released configuration need be sustained only long enough tocomplete the removal. The removal mechanism can then revert to theattached configuration, as the result of for example, cooling, pHchange, and ionic strength change, and still be replaced over the teethwithout the need to restore the released configuration.

[0016] In one embodiment, the removal mechanism may be an integralproperty of the appliance, usually being an inherent property of theshell or a part of the shell. An orthodontic appliance is provided whichhas a shell formed of at least one layer of a polymeric material. Theshell has a cavity which fits closely over a contiguous group of teeth.A contiguous group of teeth includes at least 3 teeth, but usually 4 ormore. The at least one layer of polymeric material has a first statewhere the appliance is held onto the teeth and a second state where theappliance may be removed from the teeth. The first state will exist whenthe shell is in place in the patient's mouth in the absence of any“non-oral” conditions or externally applied energy or other stimuli. Thesecond state can then be selectively induced by creating a “non-oral”environment in the patient's mouth, as discussed above. The non-oralenvironment may consist of a non-physiological temperature (above 37°C., preferably 40-55° C.; or below 37° C., preferably below 30° C.), anon-physiologic pH (above 8, preferably above 9, more preferably above8.5 or below 7, preferably below 6, more preferably below 6.5), anon-physiologic ionic strength, such as 3% sodium chloride, or the like.

[0017] In another embodiment, the removal mechanism is formed as one ormore additional component(s) or mechanism(s). Such systems will includeat least one polymeric shell which can be removably placed over apatient's teeth. The separate removal component or mechanism isswitchable from a first state to a second state.

[0018] In yet another embodiment, a dental appliance system will includea dental appliance, which has a shell with a cavity. The system willfurther include an attachment device which is formed or existsseparately from the shell. The attachment device is usually configuredto be positioned between the outer surface of the teeth and an innersurface of the cavity. The device is switchable between a first state,where the appliance is held onto the teeth, and a second state, wherethe appliance may be removed from the teeth. The switch is stimulated ormade to occur as a response to an environmental change.

[0019] In another aspect of the invention, an improved method isprovided for removing an appliance from the teeth. Preferably, theappliance is a polymeric shell, which has cavities shaped to receive andresiliently reposition teeth to produce a final tooth arrangement. In afirst aspect, the improvement comprises transforming the shell from afirst state, where the appliance is held onto the teeth, to a secondstate where the appliance may be removed from the teeth. Thetransformation is performed in situ in the patient's mouth, usually theexposure to an environmental change or external stimulus as describedabove. The transformation is repeatable so that the appliance can bereinserted.

[0020] In another aspect a method for fabricating a removableincremental tooth position adjustment appliance is provided includingforming a shell of at least one layer of a polymeric material with ateeth mold. The shell is formed with cavities shaped to receive andresiliently reposition teeth from one arrangement to a successivearrangement. The shell transforms from a first state, where theappliance is held onto the teeth, to a second state, where the appliancemay be released from the teeth.

[0021] In another aspect, an appliance system comprises a plurality ofindividual appliances that can be used for repositioning teeth from aninitial tooth arrangement to a final tooth arrangement using a pluralityof dental incremental position adjustment appliances. In thisembodiment, the plurality of position adjustment appliances will includea first appliance having a geometry selected to reposition the teethfrom the initial tooth arrangement to a first intermediate arrangement.The plurality of position adjustment appliances will also have one ormore intermediate appliances having geometries selected to progressivelyreposition the teeth from the first intermediate arrangement tosuccessive intermediate arrangements. The position adjustment applianceswill still further have a final appliance having a geometry selected toprogressively reposition the teeth from the last intermediatearrangement to the final tooth arrangement. The system will also includea removal mechanism formed into each adjustment appliance describedabove. The removal mechanism transforms from a first state to a secondstate to release each appliance from the teeth. In a preferredembodiment, the transformation is activated by a stimulus, preferably anenvironmental stimulus or condition.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 illustrates the jaw of a patient together with a dentalappliance which has been configured according to the present invention.

[0023]FIGS. 2, 2A, and 2B are cross-sectional views of embodiment forsecuring the appliance of FIG. 1 on to the teeth.

[0024]FIGS. 3, 3A, and 3B are cross-sectional views of an attachmentdevice for securing the appliance of FIG. 1 on to the teeth.

[0025] FIGS. 4A-4D are schematic illustrations of the layering geometryused in accordance with the present invention.

[0026] FIGS. 5A-5B are cross-sectional views of a process for forming anappliance in accordance with the present invention.

[0027]FIG. 6 is an illustration of a cross-sectional view of anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Referring to FIG. 1, the apparatus, systems, and methodsaccording to the present invention will include at least one appliance100 removably replaceable over the teeth. Usually, appliance 100 is oneof a plurality of incremental position adjustment appliances. Theappliances are intended to effect incremental repositioning ofindividual teeth in the jaw. The appliance 100 may be used in place ofany of the known positioners, retainers, or other removable applianceswhich are known for finishing and maintaining teeth positions inconnection with orthodontic treatment. The appliances of the presentinvention, in contrast with prior apparatus and systems, areparticularly suitable for use by a patient successively in order toachieve gradual tooth repositioning. A full description of an exemplaryrepositioning appliance is described in co-pending U.S. application Ser.No. 08/947,080(Attorney Docket No.18563-000110), filed Oct. 10, 1997,which is herein incorporated by reference for all purposes. Adescription of this exemplary dental appliance for use with the removalmechanism of the present invention is described below.

[0029] The exemplary appliance 100 includes a polymeric shell 102 havingan inner cavity 120, a proximal edge 116 and a distal edge 118. Cavity120 is shaped to receive and resiliently reposition teeth from one tootharrangement to a successive tooth arrangement. The polymeric shell willpreferably, but not necessarily, fit over all teeth present in the upperor lower jaw 114. Often, only certain one(s) of the teeth will berepositioned while others of the teeth will provide a base or anchorregion for holding the repositioning appliance in place as it appliesthe resilient repositioning force against the tooth or teeth to berepositioned. The gums and/or the palette can also serve as an anchorregion, thus allowing all or nearly all of the teeth to be repositionedsimultaneously. Additionally, anchors and adhesives, which are describedin more detail below, are available which may also serve as attachmentpoints for appliance 100. What follows is a description of variousembodiments for securing appliance 100 to the teeth.

[0030] As can be best understood with reference to FIGS. 2, 2A, and 2B,shell 102 is forced down over teeth T, typically by the patient bitingdown on the shell or by other forms of manual pressure being applied tothe shell. Edges 116 and 118 are made to engage what is known as theundercut U of the teeth. Typically, this type of engagement is helpfulin that it allows for specific tooth movements, such as extrusions (i.e.upward movement of the tooth).

[0031] Shell 102 is made of a material that has a predetermined modulus,also referred to as the stiffness, of the material. Generally, themodulus is a measurement of the inherent stiffness of a materialdetermined by conducting stress and strain tests on a material specimenand plotting the results. The value of the slope of the line generatedby the results is the modulus. The modulus can be predetermined to matchthe compliance required to reposition the teeth based on requirementsset by an individual patient's repositioning needs. In one example, theshell may have a modulus in the range of between about 0.1 GPa to 4 GPa,usually 0.5 GPa to 3 GPa, preferably about 0.8 GPa to 1.5 GPa.

[0032] Often, the shell is formed from a material that has uniformproperties, particularly stiffness, over the entire area. In some cases,however, it will be desirable to vary the stiffness, thickness, or othermaterial properties of the shell at different points or segments. Also,other layers, reinforcement elements, holes, or components may be addedto the shell to vary its stiffness and/or other mechanical properties.

[0033] The stiffness of the shell keeps edges 116 and 118 engaged withundercut U, which is designed to hold the appliance in place and effecttooth repositioning. The stiffness, however, prevents the shell frombeing easily removed from the undercut. Therefore, to reduce the effortof removing the shell from the teeth, the shell stiffness can bemodified. For instance, in the example above, to reduce the 1 to 4 GPastiffness between shell 102 and interfaces with the teeth, the stiffnessof the shell may need to be temporarily reduced by at least 10%, usuallyat least 50%, typically by approximately 10% to 90%, more typicallyabout 50% to 90%.

[0034] Once shell 102 is in position e.g. engaged with the undercut U ofthe tooth, the shell provides the desired repositioning forces to theteeth. At such time as desired, shell 102 may then be removed from theteeth. In one embodiment directed at removing the shell, shell 102 maybe made of a polymeric material which can undergo a change from a firststate to a second state. The state may include, for example a change inmaterial property or a change in shape. The changes can be made to occurthroughout the shell, but at least in the region of engagement with theundercut. The changes in material property or shape remove or reduce, asappropriate, the stiffness of the shell, which makes removal of theappliance substantially easier. The shell may include a single layer ofmaterial or else a plurality of polymeric materials. Each layer mayundergo the property change independent of one another orsimultaneously. The layer or layers may also be made of a cross-linkedpolymer capable of undergoing a change in shape. In this embodiment,shell 102 may be deformed, such that edges 116 and 118 of shell 102 canbe made to disengage undercut U, which then allows for easy removal ofappliance 100.

[0035] In an alternative embodiment, in addition to the engagement withthe undercut, or in some cases instead of the engagement with theundercut, an adhesive 122 (FIG. 2B) may be used to add holding strengthbetween appliance 100 and the teeth. The adhesive may have a peelstrength that may be reduced or eliminated in order to remove the shell.For example, in its initial state the adhesive should have a peelstrength of no less than about 250 g/cm, however, to remove the shell,the peel strength is reduced to a value below the 250 g/cm threshold.Adhesives, with compositions that are side chain crystalizable basedpolymer such as polyethylacrylate-hexadecylacrylate copolymer with XAMA2, polypentadecylacrylate with cross linker, polyoctadecylacrylate withXAMA 2, and the like, may be used for such purposes. The ability toreduce the peel strength of the adhesive, facilitates removal of theappliance. In a manner described below, the adhesive can be subjected toan environmental change (e.g. temperature) or other appropriate stimulusto reduce the peel strength. Since the peel strength can be recoveredafter the environmental change or stimulus is changed or removed, onlyone application of the adhesive to the shell may be necessary,regardless of the number of times the shell is removed from the teeth.

[0036] In another alternative embodiment, shell 102 may also be held oranchored to the teeth through an engagement between shell 102 and anattachment device such as anchor 124 (FIGS. 3, 3A and 3B). Attachmentdevice 124 may be anchored to a distal surface (between tooth and cheek)and/or a proximal surface (between tooth and tongue) of the teeth usingan adhesive or similar bonding substance. Various attachment devicedesigns are described in more detail below. Tooth anchors used withconvention wire braces are well known and described in the patent anddental literature. For use in the present invention, the anchors mayhave any of a variety of material properties with the objective being topoint a force-transmitting interface between the appliance and the toothwhen the appliance is in place. The anchors may be formed from mostsolid, physiologically acceptable materials, particularly metals,ceramics, and polymers. The materials may be rigid, resilient, orprogrammable, e.g. shape memory polymers or metal alloys. In someinstances, it is also possible that the anchors would be mechanicallycomplex, e.g. articulated, rotatable, or otherwise repositionable tofacilitate mounting or removal of the appliance from the teeth.

[0037] Attachment device 124 has an engagement surface 130 thatcorresponds to an indentation feature 128 formed on the inner surface ofcavity 120. As shell 102 is forced onto the teeth T, as described above,inner surface 126 of shell cavity 120 slidingly contacts engagementsurface 130 until indentation feature 128 matches up to engagementsurface 130. At that time, the indentation 128 conforms around the shapeof anchor 124 with a snug fit to hold shell 102 in position. As can beappreciated from the geometric shape of anchor 124 shown in FIGS. 3, 3A,and 3B, the engagement between anchor 124 and shell 102 is a “one-way”engagement, which means shell 102 is substantially locked in position.

[0038] In this alternative embodiment, anchor 124 may be made of apolymeric material that can be made to undergo a change in materialproperty. In particular, the combination of the strength of anchor 124,in an initial state, and the strength of shell 102, may be enough tohold shell 102 to the teeth, such that shell 102 may not be easilyremoved. However, as the material property of the anchor changes, thecombination of strengths is reduced. When the strength is reduced belowthe force being applied to remove shell 102, the shell lifts-off fromthe teeth. Alternatively, anchor 124 may be made of a cross-linkedpolymer. In this alternative embodiment, anchor 124 can undergo a changein shape, which changes the geometry of the anchor such that theengagement between the anchor and the shell is weakened or else removed.Although, the entire shape of the anchor may be changed, the shapechange may occur at least in the region of engagement between the anchorand the shell. The anchor may be made of a single layer or a pluralityof layers each made of a polymer or cross-linked polymer as described inmore detail below.

[0039] Shell 102 may also be configured with a reinforcement structure,such as a wire, a filament, a mesh, a ring, and/or a braid. Thereinforcement structure may also be capable of undergoing a change inmaterial property or else a change in shape, such that the changefacilitates the removal of the appliance from the teeth. For example,appliance 100 may be fabricated with a polymeric external layer and ametal inner wire embedded in at least a portion of the applianceproximate to either the engagement with the undercut or the engagementwith the anchor. The metal inner wire can be made of a memory shapemetal, such as Nitinol®, Bimetal®, Memotal® or similar alloy. The wireundergoes a change in material property (and/or shape) as it issubjected to a thermal stimulus or other external stimulus. In thisexample, the wire changes geometry. Since the wire is embedded withinthe appliance, the appliance also changes shape, which reduces theshells hold on the teeth.

[0040] In a preferred embodiment, the changes described above may beprovided through use of various polymers which undergo a glasstransition at a preselected temperature, preferably a temperature abovethe average body temperature. What follow is a description of thevarious material property and shape changes undertaken by a change inglass transition temperature.

[0041] The glass transition may occur by using a plastic, such as apolymer, that has a molecular transition incorporated in the same. Thepolymeric material is biocompatible and is formulated so that theachieved transition can be activated upon subjecting the appliance tothermal stimuli as hereinafter explained. The molecular transitions,which are incorporated in the appliance, are typically in the form ofthermotransitions, as for example, a crystalline melting point, aboveabout 37° C., preferably between 40° C. and 55° C., of the polymer sidechain, the polymer main chain, or a liquid-crystal (mesophase)transition of the polymer chain. The thermotransitions may also beaccessed via a glass transition phenomenon or a local mode moleculartransition. Examples 1-12 provide exemplary lists of such materials.

[0042] In one embodiment, a glass transition removal mechanism maycomprise a single layer or a plurality of material layers 131 configuredin shell 102, as shown in FIGS. 4A, 4B and 4C. The shell may include avariable number of layers 132, which may each have variable thicknessand/or variable glass transition temperatures. The layers may be formedin various orientations and configurations to suit the modulus andapplication requirements. The shell layers will be formed by a process,such as thermoforming or similar process, and will have formed on themthe desired shell cavities and indentations necessary for properapplication of the repositioning forces to the teeth. GLASS TRANSITIONPOLYMERS Layer Material Thickness Temp. Phase Example 1. 1 Polycarbonate 5 mils Hi Temp. 2 Polyvinyl chloride (PVC) 10 mils Low Temp. 3 PVC 10mils Low Temp. 4 PVC 10 mils Low Temp. 5 PVC 10 mils Low Temp. 6Polycarbonate  5 mils Hi Temp Example 2. 1 Polycarbonate 10 mils HiTemp. 2 PVC 10 mils Low Temp. 3 PVC 10 mils Low Temp. 4 Polycarbonate 10mils Hi Temp. Example 3. 1 PMMA  5 mils Hi Temp. 2 Polyethelyne (PE) 10mils Low Temp. 3 PE 10 mils Low Temp. 4 PE 10 mils Low Temp. 5 PE 10mils Low Temp. 6 PMMA  5 mils Hi Temp. Example 4. 1 PMMA 10 mils HiTemp. 2 PE 10 mils Low Temp. 3 PE 10 mils LowTemp. 4 PMMA 10 mils HiTemp. Example 5. 1 Polycarbonate  5 mils Hi Temp. 2 PE 10 mils Low Temp.3 PE 10 mils Low Temp. 4 PE 10 mils Low Temp. 5 PE 10 mils Low Temp. 6Polycarbonate  5 mils Hi Temp. Example 6. 1 Polycarbonate 10 mils HiTemp. 2 PE 10 mils Low Temp. 3 PE 10 mils Low Temp. 4 Polycarbonate 10mils Hi Temp. Example 7. 1 PMMA  5 mils Hi Temp. 2 PE 10 mils LowTemp. 3PE 10 mils LowTemp. 4 PE 10 mils Low Temp. 5 PE 10 mils Low Temp. 6 PMMA 5 mils Hi Temp. Example 8. 1 PMMA 10 mils HiTemp. 2 PE 10 mils LowTemp. 3 PE 10 mils LowTemp. 4 PMMA 10 mils Hi Temp. Example 9. 1Polycarbonate 20 mils Hi Temp. 2 PE 20 mils Low Temp. Example 10. 1 PMMA20 mils Hi Temp. 2 PVC 20 mils Low Temp. Example 11. 1 Polycarbonate 20mils Hi Temp. 2 PVC 20 mils Low Temp. Example 12. 1 Polysulfone 20 milsHi Temp. 2 PE 20 mils Low Temp.

[0043] In an exemplary embodiment, using the materials as in Example 1above for illustration purposes, shell 102 may include first, second,and third internal layers 132, each including 10 mils of polyvinylchloride (PVC) material, having a glass transition temperature of about50° C. Internal layers 132 are sandwiched between external layers 134,each of 5 mils of Polycarbonate material, which have a glass transitiontemperature of about 150° C. The Polycarbonate external layers 134 andthe PVC inner layers 132, while under the glass transition temperatureof both materials should have the combined modulus of all of the layersto provide the shell with the requisite modulus or strength to grab holdof and reposition the teeth. Alternatively, the inner layers may beconfigured with a higher transition temperature than that of theexternal layers. By reversing the threshold glass transitiontemperatures between the layers, the external layers can be made to losestiffness while the inner layers maintain their stiffness.

[0044] In a preferred operation, a thermal stimulus is applied to shell102. The temperature being above the glass transition temperature ofinner layers 132, but below the glass transition temperature of outerlayers 134. Once inner layers 132 reach their glass transitiontemperature, they lose stiffness, thus removing their contribution tothe stiffness of shell 102. Since, shell 102 is less stiff, theappliance can be manipulated and removed from the teeth.

[0045] External layers 134 provide a structural member or superstructurethat is kept from reaching its glass transition temperature so that itmaintains its original shape. Thus, once appliance 100 is removed fromthe teeth, the above process can be reversed. To reverse the process,inner layers 132 may be brought below their glass transitiontemperature, which will cause inner layers 132 to return to theiroriginal high stiffness state. Appliance 100 can then be re-applied tothe teeth in the manner described above and will have substantially thesame stiffness, and therefore the same effectiveness, as before theinitiation of the removal mechanism.

[0046] The glass transition removal mechanism may also comprise at leastone layer of various different homopolymers, cross-linked homopolymers,and/or copolymer blends of thermoplastics, which have a “built-in”memory capability. The materials, a representative list shown inExamples 13-21 below, are individually selected or blended together tohave a preselected glass transition temperature. As shown in FIG. 4D forillustrative purposes, the layer geometry may include a single materiallayer 132, which may range from about 1.0 mil to 60 mils, preferably10-40 mils. GLASS TRANSITION POLYMERS—CROSS-LINKED Layer MaterialThickness Temp. Phase Example 13. 1 Polycapralactone 40 mils 40-55° C.Example 14. 1 Vestenamer 40 mils 40-55° C. Example 15. 1PMMA/Polyethylene Blend 40 mils 40-55° C. Example 16. 1Polycarbonate/Polyethylene Blend 40 mils 40-55° C. Example 17. 1Polysulfone/Polyethylene Blend 40 mils 40-55° C. Example 18. 1 Polyester40 mils 40-55° C. Example 19. 1 Polyester/Polycarbonate Blend 40 mils40-55° C. Example 20. 1 Polyurathane 40 mils 40-55° C. Example 21. 1Polyurathane/Polycarbonate Blend 40 mils 40-55° C.

[0047] In FIGS. 5A and 5B, the memory removal mechanism, incorporatedinto shell 102 is shown in various stages of production. To form thememory removal mechanism, materials, such as those provided in Examples13-21, may be extruded in sheets and then formed into any shape that isdifferent, and yet approximates the general shape of the appliance.

[0048] Specifically, the cross-linked polymers may be formed into arectangular cross-sectional form 140 or alternatively, the form may beany shape, such as a dome or a flat sheet. This form is considered theinitial or first state. Form 140 may be fabricated into an appliance 142by thermoforming or similar process, with the desired surface featuresnecessary for proper application of repositioning forces to the teeth.Appliance 142 is then allowed to cool below its glass transitiontemperature, while being restrained in the desired appliance shape.Appliance 142 will maintain this shape as long as the appliance is notexposed to temperatures above the pre-set glass transition temperature.

[0049] After being secured to the teeth and upon such time when removalis desired, the single-layered shell will be subjected to a thermalstimulus which causes the material to surpass its glass transitiontemperature. The change in temperature causes appliance 142 to return toits original state (e.g. form 140). Since the original state of form 140has a different shape than appliance 142, the engagement forces arereduced.

[0050] The memory removal mechanism can be made reversible. In anexemplary embodiment, form 140 may be made of a plurality of innerlayers 150 sandwiched between an outer layer 152 as shown on appliance148, illustrated in FIG. 6. The layers may have variable thickness andvariable glass transition temperatures depending on the modulusrequirements. The internal layers 150 may be made from a homopolymer,cross-linked homopolymer, copolymer, and/or cross-linked copolymer likethose described in Examples 13-21. External layer 152 may be made of aPolycarbonate or similar material, which has a higher (or lower) glasstransition temperature then the inner layers. The layers will be formedwith the desired surface features and indentations necessary for properapplication of the repositioning forces to the teeth.

[0051] In an exemplary operation of this embodiment, after the appliancehas been applied to the teeth and upon such time as removal of theappliance is desired, a thermal stimulus is applied to shell 102. Thetemperature of the initiator is above the glass transition temperatureof inner layers 150 but below the glass transition temperature of outerlayer 152. Once inner layers 150 reach their glass transitiontemperature, they attempt to reconfigure to their original form, whileouter layers 152 continue to maintain their original shape. The internalforces generated by the attempted reconfiguration of the inner layers,push outer layers 152 outward in the direction of arrows 154 until edges116 and 118 reach positions 156. In moving the edges to positions 156, areduction in the engagement forces between appliance 148 and the teethis provided to allow for removal of the appliance.

[0052] The process may be reversed by cooling the shell below the glasstransition temperature of the inner layers 150. Outer layers 152maintain their useful shape and will continue to apply a biasing inwardforce in the direction of arrows 158 until the appliance returns to itsoriginal state.

[0053] In yet another embodiment of the glass transition removalmechanism, shown in FIGS. 3A and 3B, at least one anchor 124 may be usedto secure the appliance to the teeth. In the same manner as theappliance, anchor 124 may be made of the same polymers described above,to undergo the same types of state changes. For example, anchor 124 maycomprise a plurality of layers, but at least one layer, that include theformulations of materials in the above Examples. When subjected to athermal stimulus, anchor 124 may undergo a glass transition.Accordingly, anchor 124 may either be configured to lose strength,change shape, or both, which will facilitate removal of the shell fromthe anchor.

[0054] All of the embodiments described above may be used either incombination or independently, subject to the discretion of thepractitioner.

[0055] In each of the above described embodiments, the glass transitiontemperature is described as the threshold temperature for activating thestate change process of the appliance. However, alternatively, themelting point temperature may be used as the threshold temperature. Anadvantage to using the melting point temperature is that the change inproperties from one state to another is greater, Also, the change inproperty occurs over a smaller temperature range.

[0056] A variety of thermal stimuli have been identified which can beused to initiate the state changes in any of the embodiments describedabove. For example, the heat may be supplied to the appliance byintroducing a source of heat energy, preferably a liquid because of itsgreater heat transfer capabilities. The heated liquid causes heat torapidly transfer to the shell 102 to raise the temperature of the shelluntil the temperature reaches the transition temperature of the shell,causing the shell to transition to a second state.

[0057] Similarly magnetism, electricity, and radio waves can be used assecondary sources of heat to cause the desired state changes. Suchexternal heat can also be applied by using an infrared, microwave, orradio frequency sources as well as resistive heating. FORMULATIONS FORULTRA VIOLET AND/OR THERMALLY INITIATED POLYMERIZATION Material Percentby Weight Example 22. Methyl Methacrylate  50% Butyl Methacrylate  15%Hexyl Methacrylate  30% 1,4 Butanediol Dimethacrylate 4.6% USP 245  .4%Example 23. Isobutyl Methacrylate  30% Hexyl Methacrylate  20% OctadecylMethacrylate  22% Polyethylene Glycol Dimethacrylate  10% Perkadox 16N0.3% Methyl Methacylate  18%

[0058] Examples 22 and 23 are glass transition materials which may bepolymerized either thermally using a conventional heat source or byusing Ultra Violet (UV) light. If polymerization by UV is desired then aUV initiator such as Duracure 1173 or benzoin methylether may be addedin place of USP 245 or Perkadox 16N in Examples 22 and 23 above. Thematerials of Examples 22 and 23 may be used in the shell or in theanchor, as described above.

[0059] The removal mechanism of the present invention may also includepolymers used together to provide a formulation which changes from afirst state to a second state when subjected to an aqueous buffersolution having a predetermined pH ratio. Typical, material formulationsas shown, for example, as Examples 24-27.

[0060] Typically, when the pH sensitive appliance is applied to theteeth, shell 102 will hydrate minimally, for example up to about 10%,when exposed to the pH level of the human mouth (normal physiological pHlevel). When the appliance is to be removed, the appliance may besubjected to a solution which will cause a change in the pH ratio of themouth. Depending on the material formulation used, the change in pHcauses the appliance to hydrate, for example, up to about 90% more thanwhen at the normal pH level. When the appliance undergoes the change inhydrating states, the appliance changes dimension. For example, thelinear dimension may change from about 2% to 300% when going from alower hydration state to a higher hydration state. The swelling of theappliance removes its ability to properly engage the teeth. FORMULATIONSFOR CHANGES BY ABSORPTION OF A LIQUID Material Percent by Weight Example24. N-Vinyl Pyrrolidone  25% Butyl Acrylate  40% Isobornyl Methacrylate 30% 1,6-Hexane Dioldimethacrylate   5% Azobis Isobutyl Nitrile 0.5%Example 25. 2-Hydroxy Ethylmethacrylate  45% Methyl Methacrylate  35%Butyl Methacrylate  15% Polyethylene Glycoldimethacrylate   5% BenzoylPeroxide 0.5% Example 26. Methacrylic Acid  20% Methyl Methacrylate  40%Octadecyl Methacrylate  35% Ethylene Glycoldimethacrylate   5% AzobisIsobutyl Nitrile 0.5% Example 27. Acrylic Acid  20% Methyl Methacrylate 40% Octadecyl Methacrylate  35% Ethylene Glycoldimethacrylate   5%Azobis Isobutyl Nitrile 0.5%

[0061] Alternatively, the anchor attachment may be made from thematerials, such as those listed in Examples 24-27 and may be made toundergo a hydration state change when subjected to a different pH ratio.In one embodiment, while at the normal pH level, the attachment devicemay swell to a size that facilitates the engagement between theappliance and the teeth. For example, the hydration of the anchor may beup to about 90%. When the attachment device is exposed to a different pHlevel, the attachment device will dehydrate and shrink to disengage fromthe appliance. The range of dimensional change depends on the attachmentdevice material composition, but will nonetheless be sufficient to allowfor removal of the appliance. As before, the change in the applianceproperties and in the attachment device may take place together orindependently.

[0062] The removal mechanism may also respond to a state change causedby ionic strength changes, which causes water absorption in polymerssubjected to different concentration of salts, including NaCl or sugar.

[0063] Typically, when the appliance is applied to the teeth, the shellwill hydrate minimally, for example up to about 10%, based on theaverage concentration of salts in the human mouth (normal ionicstrength). When the appliance is to be removed, the appliance may besubjected to a solution which will cause a change in the concentrationof the salts. Depending on the material formulation used, the change insalt concentration causes the appliance to hydrate, for example, up toabout 90% more than when in the normal concentration ranges. Exemplarymaterial formulations are described in Examples 28 and 29. When theappliance undergoes the change in hydrating states, the appliancechanges dimension. For example, the linear dimension may change fromabout 2% to 300% when going from a lower hydration state to a higherhydration state. FORMULATION FOR CHANGES BY ABSORPTION OF A LIQUID INDIFFERENT IONIC STRENGTH CONDITIONS Material Percent by Weight Example28. N-Vinyl Pyrrolidone  25% Butyl Acrylate  40% Isobornyl Methacrylate 30% 1,6-Hexane Dioldimethacrylate   5% Azobis Isobutyl Nitrile 0.5%Example 29. 2-Hydroxy Ethylmethacrylate  45% Methyl Methacrylate  35%Butyl Methacrylate  15% Polyethylene Glycoldimethacrylate   5% BenzoylPeroxide 0.5%

[0064] Alternatively, the anchor attachment may also be made frommaterials in Examples 28 and 29 and may undergo a hydration state changewhen subjected to a different concentration of salts. While in itsinitial state, the attachment device may swell to a size thatfacilitates the engagement between the appliance and the teeth. Forexample, the hydration of the anchor may be up to about 90%. When theattachment device is exposed to a different concentration of salts, theattachment device will dehydrate and shrink to disengage from theappliance. The range of dimensional change depends on the attachmentdevice material composition. As before, the change in the applianceproperties and in the attachment device may take place together orindependently.

[0065] While the above is a complete description of the preferredembodiments of the invention, various alternatives, modifications, andequivalents may be used. In one example, appliance 100 may be removedfrom the teeth when a pressure is directed down on the top surface ofthe teeth, either through biting down or through a direct manualapplication of the pressure. The pressure may force edges 116 and 118 inan outward direction, thus removing engagement between the appliance andinterfaces on the teeth.

[0066] Therefore, the above description should not be taken as limitingthe scope of the invention which is defined by the appended claims.

What is claimed is:
 1. A system of dental positioning adjustmentappliances comprising: a plurality of incremental position adjustmentappliances, each of said appliances comprising: a shell including atleast one layer of a polymeric material and having a cavity which fitsclosely over a contiguous group of teeth, the at least one layer ofpolymeric material having a first state where the appliance is held ontothe teeth and a second state where the appliance may be removed from theteeth.
 2. A system as in claim 1, wherein the polymeric material existsin the second state when exposed to a non-oral environment.
 3. A systemas in claim 2, wherein the non-oral environment is selected from thegroup consisting of non-physiologic temperature, non-physiologic pH, andnon-physiologic ionic strength.
 4. A system as in claim 1, wherein thepolymeric material is converted to the second state by exposure toenergy selected from the group consisting of mechanical energy andelectromagnetic energy.
 5. A system as in claim 1, wherein the shell hascavities shaped to receive and resiliently reposition teeth from onearrangement to a successive arrangement.
 6. A system as in claim 1,wherein the at least one layer comprises a material selected from thegroup consisting of memory polymers, methacrylate containing polymers,acrylate containing polymers, thermoplastic polymers, cross-linkedthermoplastic polymers, thermoplastic polymer blends, cross-linkedthermoplastic polymer blends, thermoplastic elastomer polymers, andthermoset polymers.
 7. A system for repositioning teeth comprising: aplurality of incremental position adjustment appliances, each of saidappliances comprising: a polymeric shell having cavities shaped toreceive and resiliently reposition teeth from one arrangement to asuccessive arrangement; and a removal mechanism coupled to each of thepolymeric shells, the removal mechanism being switchable from a firststate where the shell is held onto the teeth to a second state where theshell may be removed from the teeth.
 8. A system as in claim 7, whereinthe removal mechanism comprises at least one polymeric layer laminatedto at least a portion of the polymeric shell.
 9. A system as in claim 8,wherein the polymeric layer comprises a material selected from the groupconsisting of memory polymers, methacrylate containing polymers,acrylate containing polymers, thermoplastic polymers, cross-linkedthermoplastic polymers, thermoplastic polymer blends, cross-linkedthermoplastic polymer blends, thermoplastic elastomer polymers, andthermoset polymers.
 10. A system as in claim 7, wherein the removalmechanism comprises a plurality of polymeric layers laminated to theshell, wherein at least one of the plurality of layers undergoes thestate switch.
 11. A system as in claim 7, wherein the removal mechanismcomprises a plurality of polymeric layers laminated to the shell,wherein each layer undergoes the state switch independent of the otherlayers.
 12. A system as in claim 7, wherein the removal mechanismcomprises an adhesive within at least a portion of the cavities, theadhesive having a first peel strength when in the first state and asecond peel strength when in the second state.
 13. A system as in claim7, wherein the removal mechanism is formed at least in part from amaterial having a first state with a first modulus and a second statewith a second modulus, the first modulus being different from the secondmodulus.
 14. A system as in claim 7, wherein the removal mechanism is astructure, the structure having a first state with a first deformationand a second state with a second deformation, the first deformationbeing different from the second deformation.
 15. A system as in claim 7,wherein the removal mechanism switches from the first state to thesecond state in response to an environmental stimulus.
 16. A system asin claim 15, wherein the environmental stimulus is selected from thegroup consisting of temperature, ionic strength, pH ratio, and liquidabsorption.
 17. A system as in claim 7, wherein the removal mechanismswitches from the first state to the second state in response to anexternal stimulus.
 18. A system as in claim 17, wherein the externalstimulus is selected from the group consisting of light, magnetism,electricity, and radio waves.
 19. A system as in claim 1, wherein atleast a portion of the shell has a stiffness in the range from 0.1 GPato 4 GPa in the first state and wherein the stiffness is reduced by atleast 10% in the second state.
 20. A system as in claim 19, wherein atleast a portion of the shell has a stiffness in the range from 0.1 GPato 4 GPa in the first state and wherein the stiffness is reduced by atleast 90% in the second state.
 21. A system for repositioning teethcomprising: a plurality of incremental position adjustment appliances,each of said appliances comprising; a polymeric shell having a cavityshaped to receive and resiliently reposition teeth from one arrangementto a successive arrangement; and an attachment device which couples tothe shell of each shell, the attachment device having a first statewhere the shell is held onto the teeth and a second state where theshell may be removed from the teeth.
 22. A system as in claim 21,wherein the attachment device is positionable between an outer surfaceof the teeth and an inner surface of the cavity.
 23. A system as inclaim 21, wherein the attachment device is an anchor device.
 24. Asystem as in claim 23, wherein the anchor comprises a geometric shape,the geometric shape allowing installation of the shell on to the teethand restricting removal of the shell when the anchor device is in thefirst state.
 25. A system as in claim 21 wherein the attachment devicecomprises at least one polymeric layer laminated to at least a portionof the attachment device.
 26. A system as in claim 25, wherein thepolymeric layer comprises a material selected from the group consistingof memory polymers, methacrylate containing polymers, acrylatecontaining polymers, thermoplastic polymers, cross-linked thermoplasticpolymers, thermoplastic polymer blends, cross-linked thermoplasticpolymer blends, thermoplastic elastomer polymers, and thermosetpolymers.
 27. A system as in claim 21, wherein the attachment devicecomprises a plurality of polymeric layers laminated to the attachmentdevice, wherein at least one of the plurality of layers undergoes thestate switch.
 28. A system as in claim 21, wherein the attachment devicecomprises a plurality of polymeric layers laminated to the attachmentdevice, wherein each layer undergoes the state switch independent of theother layers.
 29. A system as in claim 21, wherein the attachment deviceswitches from the first state to the second state in response to anenvironmental stimulus.
 30. A system as in claim 29, wherein theenvironmental stimulus is selected from the group consisting oftemperature, ionic strength, pH ratio, and liquid absorption.
 31. Asystem as in claim 21, wherein the attachment device switches from thefirst state to the second state in response to an external stimulus. 32.A system as in claim 31, wherein the external stimulus is selected fromthe group consisting of light, magnetism, electricity, and radio waves.33. A system as in claim 21, wherein the attachment device is embeddedwithin the shell.
 34. A system as in claim 33, wherein the attachmentdevice is a structure selected from the group consisting of wires,filaments, meshes, rings, and braids.
 35. A system as in claim 33,wherein at least a portion of the attachment device comprises a shapememory alloy, the alloy being reconfigured when subjected to an externalstimulus.
 36. A system comprising:. a plurality of incremental positionadjustment appliances, each of said appliances comprising; a shellincluding at least one layer of a polymeric material and having a cavitywhich fits closely over a contiguous group of teeth; and an attachmentdevice coupled to each shell and positionable between an outer surfaceof the teeth and an inner surface of the cavity, the at least one layerof polymeric material and the attachment device each having a firststate where the shell is held onto the teeth and a second state wherethe shell may be removed from the teeth.